High-toughness seamless steel pipe for automobile bumper and method for manufacturing the same

Abstract

This invention provides a high-strength and high-toughness seamless steel tube for automotive bumper poles and its manufacturing method. The high-strength and high-toughness seamless steel tube for automotive bumper poles comprises an Fe base and chemical elements dispersed in the Fe base in the following mass percentages: C: 0.08–0.22, Si: 0.1–0.45, Mn: 1–1.8, Ni: 0.1–0.6, Cr: 0.05–1, Ti: 0.01–0.05, B: 0.005–0.02, Cu: 0.05–0.5, Al: 0.015–0.06, Nb: 0.01–0.1, N: 0.005–0.015. The high-strength and high-toughness seamless steel tube for automotive bumper poles of this invention exhibits good comprehensive mechanical properties and high dimensional accuracy, especially good straightness, enabling accurate fit with connecting components.

Description

Technical Field

[0001] This invention relates to the field of metallurgical technology, specifically to a high-strength and tough seamless steel pipe for automobile anti-collision bars and its manufacturing method. Background Technology

[0002] In vehicle structural design, anti-collision plates or anti-collision bars are usually added to the doors to improve their collision resistance and rigidity. The mechanical properties of the anti-collision plates or anti-collision bars directly determine the safety factor of the vehicle. Therefore, vehicle anti-collision plates or anti-collision bars need to have high strength and hardness, and at the same time, they are required to withstand large impact forces. Therefore, the tensile properties, impact toughness and hardness of vehicle anti-collision plates or anti-collision bars must be within a reasonable range to meet their usage requirements. At the same time, they also need to ensure good weldability and high dimensional accuracy.

[0003] The invention patent with publication number CN101497960A and publication date August 5, 2009, entitled "A High-Strength Anti-collision Tube for Automobiles and Its Manufacturing Method", discloses a processing and manufacturing method for a tube used in anti-collision bars. Its chemical composition is C: 0.15-0.25%, Mn: 0.8-1.5%, Si: 0.2-0.5%, Ti: 0.01-0.04%, B: 0.001-0.004%, V≤0.05-0.15%, 0.008%<N≤0.015%. This invention patent discloses a processing and manufacturing method for an anti-collision bar with a tensile strength that can exceed 1500MPa. However, its impact performance is low, with a Charpy longitudinal impact energy KV2 of 80-90J at room temperature, which cannot meet the requirements of high strength and high toughness of anti-collision bars. Summary of the Invention

[0004] In view of this, the present invention provides a high-strength and high-toughness seamless steel tube for automotive anti-collision bars with high strength, hardness and good impact resistance.

[0005] The present invention also provides a method for manufacturing a high-strength and tough seamless steel tube for automotive anti-collision bars.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] According to a first aspect of the present invention, a high-strength and high-toughness seamless steel tube for automotive anti-collision bars comprises an Fe base and chemical elements dispersed in the Fe base in the following mass percentages: C: 0.08%–0.22%, Si: 0.1%–0.45%, Mn: 1.0%–1.8%, Ni: 0.1%–0.6%, Cr: 0.05%–1.0%, Ti: 0.01%–0.05%, B: 0.005%–0.02%, Cu: 0.05%–0.50%, Al: 0.015%–0.060%, Nb: 0.01%–0.1%, N: 0.005%–0.015%.

[0008] According to another embodiment of the present invention, a high-strength and high-toughness seamless steel tube for automotive anti-collision bars is composed of an Fe base and chemical elements dispersed in the Fe base in the following mass percentages: C: 0.08%–0.22%, Si: 0.1%–0.45%, Mn: 1.0%–1.8%, Ni: 0.1%–0.6%, Cr: 0.05%–1.0%, Ti: 0.01%–0.05%, B: 0.005%–0.02%, Cu: 0.05%–0.50%, Al: 0.015%–0.060%, Nb: 0.01%–0.1%, N: 0.005%–0.015%, with the balance being unavoidable impurities.

[0009] Furthermore, the unavoidable impurities include P and S, wherein, by mass percentage, P ≤ 0.025% and S ≤ 0.015%.

[0010] Furthermore, the mass percentages of the chemical elements also satisfy the following conditions: Ti / N > 2, Nb / N > 2.

[0011] Furthermore, the microstructure of the seamless steel pipe consists of ferrite, pearlite, and dispersed precipitates.

[0012] Furthermore, the precipitated phase includes Ti(CN) and Nb(CN).

[0013] Furthermore, the seamless steel pipe has a tensile strength ≥1200 MPa, an elongation ≥15%, a Charpy longitudinal impact energy KV2 ≥150 J at room temperature, a Vickers hardness of 490~600 HV on the surface, and a Vickers hardness difference of <30 HV.

[0014] Furthermore, the wall thickness of the seamless steel pipe is 1 to 2.5 mm.

[0015] Furthermore, the outer diameter of the seamless steel pipe is 15–30 mm.

[0016] Furthermore, the straightness of the seamless steel pipe is <0.1mm / m.

[0017] A method for manufacturing a high-strength, high-toughness seamless steel tube for an automobile anti-collision bar according to another embodiment of the present invention includes the following steps:

[0018] S1, according to the above chemical element composition, is mixed and then smelted to obtain tube blank;

[0019] S2, perform hot piercing treatment on the tube blank in step S1, with a heating temperature of 1220~1260℃ and a holding time of 10~20min;

[0020] S3, the tube blank after hot piercing in step S2 is placed on a tension reducing machine for diameter reduction and wall thickness reduction, and after natural cooling to room temperature, a precast steel pipe is obtained.

[0021] S4, perform pretreatment on the precast steel pipe from step S3, the pretreatment including:

[0022] The precast steel pipe in step S3 is subjected to pickling, annealing, phosphating and saponification in sequence. In the annealing process, the annealing temperature is 680-850℃ and the holding time is 20-70min.

[0023] Furthermore, the manufacturing method of the high-strength and high-toughness seamless steel tube for automobile anti-collision bars in this embodiment of the invention may further include:

[0024] S5. Perform cold working on the prefabricated steel pipe from step S4 in one or more passes to obtain a seamless steel pipe with an outer diameter of 15-30 mm and a wall thickness of 1-1.5 mm. The elongation coefficient of each cold working pass is ≤1.8.

[0025] Furthermore, the manufacturing method of the high-strength and high-toughness seamless steel tube for automobile anti-collision bars in this embodiment of the invention may further include:

[0026] S6, while rotating the seamless steel pipe from step S5, high-frequency induction hardening is performed, wherein the hardening temperature is 860-950℃, the temperature is held for 8-20 minutes and then water-cooled to room temperature, the rotation speed of the seamless steel pipe is 60-150 r / min, and the forward speed is 0.05-0.2 m / s.

[0027] The tempering temperature is 150-400℃, and the temperature is maintained for 10-40 minutes before air cooling to room temperature.

[0028] The above-described technical solution of the present invention has at least one of the following beneficial effects:

[0029] According to an embodiment of the present invention, the high-strength and high-toughness seamless steel tube for automobile anti-collision bars, through composition design and optimized manufacturing process, that is, based on the chemical element composition of the present invention, combined with the manufacturing process of pre-treating the prefabricated steel tube before cold working and performing high-frequency induction hardening treatment on the seamless steel tube after cold working, can form a microstructure with ferrite, pearlite and dispersed precipitates. The dispersed precipitates can improve the strength and impact resistance of the seamless steel tube through the grain refinement strengthening effect. The final seamless steel tube has a tensile strength ≥1200 MPa, an elongation ≥15%, a room temperature Charpy longitudinal impact energy KV2 ≥150 J, and a surface Vickers hardness of 490~600 HV.

[0030] Furthermore, based on high-speed rotation and forward movement, high-frequency induction hardening is performed to obtain seamless steel pipes with a straightness of <0.1mm / m and a surface Vickers hardness difference of <30HV. The pipes have high dimensional accuracy, especially good straightness, which can achieve accurate fit with connecting parts. Attached Figure Description

[0031] Figure 1 This is a metallographic image of a high-strength and high-toughness seamless steel tube for an automobile anti-collision bar according to Embodiment 1 of the present invention. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention are within the scope of protection of the present invention.

[0033] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, the terms "an" or "a" and similar terms do not indicate a quantity limitation, but rather indicate the presence of at least one. The terms "connected" or "linked" and similar terms are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. "Up," "down," "left," "right," etc., are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship also changes accordingly.

[0034] The following is a detailed description of the high-strength and high-toughness seamless steel tube (hereinafter referred to as seamless steel tube) used in the automotive anti-collision bar according to an embodiment of the present invention.

[0035] The seamless steel pipe according to embodiments of the present invention comprises an Fe base and chemical elements dispersed in the Fe base in the following mass percentages: C: 0.08%–0.22%, Si: 0.1%–0.45%, Mn: 1.0%–1.8%, Ni: 0.1%–0.6%, Cr: 0.05%–1.0%, Ti: 0.01%–0.05%, B: 0.005%–0.02%, Cu: 0.05%–0.50%, Al: 0.015%–0.060%, Nb: 0.01%–0.1%, N: 0.005%–0.015%.

[0036] In other words, by designing the composition of the above chemical elements, seamless steel pipes with a microstructure of ferrite, pearlite and dispersed precipitates can be formed. The precipitates containing Ti(CN) and Nb(CN) can play a role in grain refinement and strengthening, which can improve the strength and impact resistance of seamless steel pipes.

[0037] Furthermore, the seamless steel pipe is composed of Fe-based elements and chemical elements dispersed in the Fe-based element in the following mass percentages: C: 0.08%–0.22%, Si: 0.1%–0.45%, Mn: 1.0%–1.8%, Ni: 0.1%–0.6%, Cr: 0.05%–1.0%, Ti: 0.01%–0.05%, B: 0.005%–0.02%, Cu: 0.05%–0.50%, Al: 0.015%–0.060%, Nb: 0.01%–0.1%, N: 0.005%–0.015%, with the balance being unavoidable impurities. In other words, the seamless steel pipe uses Fe as its main constituent element, and by adjusting the mass percentage of beneficial elements and controlling the content of unavoidable impurities, the strength and impact resistance of the seamless steel pipe are improved.

[0038] Specifically, the design principles of each chemical element in the seamless steel pipe of this invention are as follows:

[0039] Carbon (C) is one of the main elements that improve the strength of steel. It can effectively increase the strength of steel through the formation of carbides, and its addition cost is low. When the C content is too low, it will reduce the tensile strength of the steel pipe, but when the C content is too high, the overall properties of the seamless steel pipe, such as toughness, impact performance, and weldability, will be affected.

[0040] Therefore, in this invention, for seamless steel pipes with tensile strength ≥1200 MPa, elongation ≥15%, and room temperature Charpy longitudinal impact energy KV2 ≥150 J, the mass percentage of C in the seamless steel pipe is controlled between 0.08% and 0.22%.

[0041] Si: Si acts as a reducing agent and deoxidizer in the steelmaking process. It has a high solid solubility in steel and can strengthen the ferrite in the steel to improve its strength. However, excessive Si content will reduce the toughness of steel pipes, especially the low-temperature impact toughness, and will also reduce the weldability of the steel pipes.

[0042] Therefore, in this invention, for seamless steel pipes with tensile strength ≥1200 MPa, elongation ≥15%, and room temperature Charpy longitudinal impact energy KV2 ≥150 J, the mass percentage of Si in the seamless steel pipe is controlled between 0.1% and 0.45%.

[0043] Mn: Mn is an important alloying element and a weak carbide-forming element. Mn mainly improves the strength of steel through solid solution strengthening. However, excessive Mn content will lower the phase transformation temperature of steel, reduce the critical cooling rate for quenching, increase the hardenability of steel, and reduce impact toughness.

[0044] Therefore, in this invention, for seamless steel pipes with tensile strength ≥1200 MPa, elongation ≥15%, and room temperature Charpy longitudinal impact energy KV2 ≥150 J, the mass percentage of Mn in the seamless steel pipe is controlled at 1.0% to 1.8%.

[0045] Ni: Ni can improve the strength and hardenability of steel, as well as its toughness. Appropriate amounts of Ni can be combined with other alloying elements to achieve ideal strengthening effects while simultaneously improving the toughness of the steel.

[0046] Therefore, in this invention, for seamless steel pipes with tensile strength ≥1200 MPa, elongation ≥15%, and room temperature Charpy longitudinal impact energy KV2 ≥150 J, the mass percentage of Ni in the seamless steel pipe is controlled at 0.1% to 0.6%.

[0047] Cr: Cr is a medium-strong carbide-forming element. Some Cr in steel can replace iron to form alloy cementite, improving its stability; another portion of Cr can dissolve in ferrite, acting as a solid solution strengthening agent, increasing the strength and hardness of the ferrite. It can also improve the hardenability of the steel. However, excessive Cr content can affect the toughness of welded parts.

[0048] Therefore, in this invention, for seamless steel pipes with a microstructure of ferrite, pearlite and dispersed precipitates, the mass percentage of Cr in the seamless steel pipe is controlled at 0.1% to 0.6%.

[0049] Ti: Ti is a strong carbide that can combine with C and N in steel to form compounds, significantly improving the strength of the steel. Ti can also combine with B to improve the hardenability of the steel. However, if the Ti content is too high, it is easy to form more dot-chain TiN inclusions, which affects the impact performance of the steel and makes it more prone to cracking during service.

[0050] Therefore, in this invention, for seamless steel pipes with a microstructure of ferrite, pearlite and dispersed precipitates, the mass percentage of Ti in the seamless steel pipe is controlled at 0.01% to 0.05%.

[0051] Nitrogen (Nb): Nb's role is to improve the toughness of steel, and an appropriate amount of Nb can significantly improve the toughness of steel. In addition, Nb can combine with C and N in steel to form compounds, which can significantly improve the strength of steel. However, excessive Nb content will reduce the toughness of steel.

[0052] Therefore, in this invention, for seamless steel pipes with a microstructure of ferrite, pearlite and dispersed precipitates, the mass percentage of Nb in the seamless steel pipe is controlled at 0.01% to 0.1%.

[0053] B: The main function of B is to improve the hardenability of steel, so that the steel has higher strength and hardness after quenching, and thus has good comprehensive properties after tempering.

[0054] Therefore, in this invention, for seamless steel pipes with tensile strength ≥1200 MPa, elongation ≥15%, and room temperature Charpy longitudinal impact energy KV2 ≥150 J, and based on cost factors and the manufacturability of steel, the mass percentage of B in the seamless steel pipe is controlled at 0.005% to 0.02%.

[0055] Cu: Cu can enhance the toughness of steel. However, excessive Cu content can affect the hot working properties of steel.

[0056] Therefore, in this invention, for seamless steel pipes with tensile strength ≥1200 MPa, elongation ≥15%, and room temperature Charpy longitudinal impact energy KV2 ≥150 J, the mass percentage of Cu in the seamless steel pipe is controlled between 0.05% and 0.50%.

[0057] Al: Al acts as a deoxidizer in steel and helps improve its toughness and workability. Appropriate Al content can significantly improve the toughness and workability of steel. However, excessive Al content increases the tendency for cracks to form in the steel.

[0058] Therefore, in this invention, for seamless steel pipes with tensile strength ≥1200 MPa, elongation ≥15%, and room temperature Charpy longitudinal impact energy KV2 ≥150 J, and based on the manufacturability of seamless steel pipes, the mass percentage of Al in the seamless steel pipe is controlled between 0.015% and 0.060%.

[0059] Nitrogen (N) is mainly used to combine with Nb or Ti to form fine, dispersed strengthening compounds, which can increase the strength and impact toughness of steel. However, excessively high N content can lead to the formation of more inclusions when N combines with alloying elements, resulting in a decrease in the impact performance of the steel.

[0060] Therefore, in this invention, for seamless steel pipes with a microstructure of ferrite, pearlite and dispersed precipitates, the mass percentage of N in the seamless steel pipe is controlled between 0.005% and 0.015%.

[0061] Furthermore, unavoidable impurities include phosphorus (P) and sulfur (S), with P ≤ 0.025% and S ≤ 0.015% by mass percentage. In other words, by controlling the addition of harmful elements P and S in seamless steel pipes, the mechanical properties of the seamless steel pipes can be improved. Specifically, S is an impurity introduced into the steel by pig iron and fuel; sulfides formed during steel production reduce the mechanical properties of the steel, and hot-working fibrous structures are formed during rolling. P is an impurity introduced into the steel by pig iron; P can completely dissolve in ferrite, reducing the plasticity and toughness of the steel.

[0062] Furthermore, the mass percentages of chemical elements also satisfy the following conditions: Ti / N > 2, Nb / N > 2. In other words, by further controlling the mass percentage ratios of Ti and N, and Nb and N, Nb and Ti can combine with N to form fine, dispersed strengthening compounds, increasing the strength and impact toughness of the seamless steel pipe. This avoids excessive N combining with alloying elements, generating inclusions, and reducing the impact performance of the seamless steel pipe.

[0063] Therefore, in this invention, for seamless steel pipes with a microstructure of ferrite, pearlite and dispersed precipitates, the Ti / N ratio in the seamless steel pipe is controlled to be >2 by mass percentage, and the Nb / N ratio is controlled to be >2 by mass percentage.

[0064] Furthermore, the microstructure of seamless steel pipes consists of ferrite, pearlite, and dispersed precipitates. That is to say, as... Figure 1 The diagram shows a high-strength and high-toughness seamless steel tube for automotive anti-collision bars according to an embodiment of the present invention. Through the above-mentioned chemical element composition design, a seamless steel tube with a microstructure of ferrite, pearlite and dispersed precipitates can be obtained. This seamless steel tube has high strength and good impact resistance.

[0065] Furthermore, the precipitated phases include Ti(CN) and Nb(CN). The precipitated phases including Ti(CN) and Nb(CN) are fine and dispersed strengthening compounds, which can increase the strength and impact toughness of seamless steel pipes.

[0066] Furthermore, the seamless steel pipe has a tensile strength ≥1200 MPa, elongation ≥15%, Charpy longitudinal impact energy at room temperature KV2 ≥150 J, surface Vickers hardness of 490~600 HV, and surface Vickers hardness difference <30 HV. In other words, through the above composition design, a seamless steel pipe with high strength and good impact resistance can be obtained.

[0067] Furthermore, the wall thickness of the seamless steel pipe is 1–2.5 mm. This is based on the mechanical performance requirements and manufacturing cost considerations when seamless steel pipes are used as automotive anti-collision bars.

[0068] Furthermore, the outer diameter of the seamless steel tube is 15–30 mm. This is based on the mechanical performance requirements and manufacturing cost considerations when seamless steel tubes are used as automotive crash bars.

[0069] Furthermore, the straightness of the seamless steel pipe is <0.1mm / m. In other words, a straightness of <0.1mm / m can further improve the strength and impact resistance of the seamless steel pipe.

[0070] Furthermore, the manufacturing method of the high-strength and high-toughness seamless steel tube for automobile anti-collision bars according to the second aspect of the present invention includes the following steps:

[0071] S1, according to the above chemical element composition, is mixed and then smelted to obtain tube blank;

[0072] S2, hot piercing treatment is performed on the tube blank in step S1, with a heating temperature of 1220~1260℃ and a holding time of 10~20min;

[0073] S3, the tube blank after hot piercing in step S2 is placed on a tension reducing machine for diameter and wall thickness reduction, and then naturally cooled to room temperature to obtain a seamless steel pipe.

[0074] S4, perform pretreatment on the precast steel pipe from step S3. The pretreatment includes:

[0075] The precast steel pipe in step S3 is subjected to pickling, annealing, phosphating and saponification in sequence. In the annealing process, the annealing temperature is 680-850℃ and the holding time is 20-70min.

[0076] In other words, for the seamless steel pipe of the present invention, by designing the composition, controlling the heating temperature and holding time during the hot piercing process, and reducing the diameter and wall thickness, a microstructure of ferrite, pearlite and dispersed precipitates is finally formed, resulting in a high-strength and high-toughness seamless steel pipe for automobile anti-collision bars with high strength, hardness and impact resistance, as well as dimensional accuracy and convenient assembly.

[0077] More specifically, in step S4, pickling removes the oxide layer from the surface of the precast steel pipe and passivates its surface, improving its corrosion resistance. After pickling, the precast steel pipe undergoes annealing. By controlling the annealing temperature to 680–850°C and the holding time to 20–70 minutes, the plasticity of the precast steel pipe is improved, facilitating subsequent cold working. The grain size is also adjusted, further enhancing its mechanical properties. Next, phosphating is performed, forming a protective phosphate film on the surface of the precast steel pipe to prevent corrosion. This protective film also acts as a lubricant, reducing the coefficient of friction on the cold-worked surface and minimizing product defects caused by cold working. Finally, saponification further reduces the coefficient of friction on the cold-worked surface, further lowering the defect rate.

[0078] Furthermore, the manufacturing method of the high-strength and high-toughness seamless steel tube for automobile anti-collision bars in this embodiment of the invention may further include: S5, performing cold working on the prefabricated steel tube from step S4 in one or more passes to obtain a seamless steel tube with an outer diameter of 15-30 mm and a wall thickness of 1-1.5 mm, wherein the elongation coefficient of each cold working pass is ≤1.8. In other words, based on the above chemical element ratios, by controlling the elongation coefficient of each cold working pass, the dimensional accuracy of the prefabricated steel tube is further improved, ultimately obtaining a seamless steel tube with an outer diameter of 15-30 mm and a wall thickness of 1-1.5 mm.

[0079] Furthermore, the manufacturing method of the high-strength and high-toughness seamless steel tube for automotive anti-collision bars in this embodiment of the invention may further include: S6, rotating the seamless steel tube from step S5 while performing high-frequency induction hardening treatment, wherein the quenching temperature is 860-950℃, held for 8-20 minutes and then water-cooled to room temperature, the rotation speed of the seamless steel tube is 60-150 r / min, the forward speed is 0.05-0.2 m / s, the tempering temperature is 150-400℃, held for 10-40 minutes and then air-cooled to room temperature. In other words, by heat-treating the seamless steel tube through high-frequency induction hardening treatment, combined with the aforementioned chemical element composition of the seamless steel tube, controlling the quenching and tempering parameters can improve hardenability, further enhancing the strength and mechanical properties of the seamless steel tube. Furthermore, by performing high-frequency induction heating and quenching on the seamless steel tube in a high-speed rotating and forward manner, controlling the rotation speed and forward speed of the seamless steel tube can further improve the dimensional accuracy of the seamless steel tube, resulting in a seamless steel tube with uniform hardness and good straightness.

[0080] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below.

[0081] Examples 1-10 and Comparative Examples 1-6

[0082] The seamless steel pipes of Embodiments 1-10 of the present invention are obtained by the following steps:

[0083] (1) Calculate the margin of the iron billet according to the components and component content shown in Table 1. The content of unavoidable impurities in the iron billet should be taken into account during the calculation. Then, smelting is carried out to obtain the tube blank.

[0084] (2) Heat the tube blank to the heating temperature in Table 2, and keep the tube blank at the heating and holding time in Table 2, and then perform hot piercing treatment on the tube blank.

[0085] (3) The hot-pierced tube blank is placed on a tension reducing machine for diameter and wall thickness reduction, and then naturally cooled to room temperature to obtain a precast steel pipe.

[0086] (4) Pretreatment of the precast steel pipe includes pickling, annealing, phosphating and saponification in sequence. The annealing parameters are as shown in Table 2.

[0087] Subsequently, the prefabricated steel pipe is subjected to one or more cold working processes to obtain seamless steel pipe;

[0088] (5) For the seamless steel pipe after cold working, high frequency induction hardening is carried out by high-speed rotation. The rotation speed, forward speed and high frequency induction hardening process parameters of the seamless steel pipe are specified in Table 3.

[0089] The steel pipes of Comparative Examples 1-6 were also manufactured according to the components and component contents shown in Table 1, and using the same manufacturing process as the embodiments of the present invention, with each process parameter according to Table 2-3.

[0090] Specifically, Table 1 lists the composition and mass ratios of Ti to N and Nb to N for the seamless steel pipes of Examples 1-10 and Comparative Examples 1-6. Tube blanks were prepared according to the chemical elemental composition in Table 1.

[0091] Table 1. Composition (wt.%) and mass ratios of Ti to N and Nb to N for the seamless steel pipes of Examples 1-10 and the steel pipes of Comparative Examples 1-6.

[0092]

[0093] Table 2 lists the main process parameters for the hot piercing step and the main process parameters for the annealing treatment before cold working in Examples 1-10 and Comparative Examples 1-6. Seamless steel pipes of Examples 1-10 and steel pipes of Comparative Examples 1-6 can be obtained according to the main process parameters in Table 2.

[0094] Table 2 shows the main process parameters for the hot piercing step and the main process parameters for the annealing treatment in the cold working step of Examples 1-10 and Comparative Examples 1-6.

[0095]

[0096]

[0097] Table 3 lists the main process parameters for the heat treatment steps of Examples 1-10 and Comparative Examples 1-6. Seamless steel pipes of Examples 1-10 and steel pipes of Comparative Examples 1-6 can be produced according to the main process parameters in Table 3.

[0098] Table 3. Main process parameters for the heat treatment steps in Examples 1-10 and Comparative Examples 1-6

[0099]

[0100]

[0101] The seamless steel tubes of this invention can be used to manufacture automotive anti-collision bars. To verify their mechanical properties, samples were taken from the seamless steel tubes of Examples 1-10 and Comparative Examples 1-6. The impact test used a 2mm*10mm*55mm arc-shaped specimen with a V-notch, a notch depth of 2mm, and a blade radius of 2mm. Tensile tests, impact tests, hardness tests, and straightness measurements were then performed on the seamless steel tubes of Examples 1-10. The user's standards for seamless steel tubes used in automotive stabilizer bars are as follows: A: Tensile strength ≥ 1200 MPa; B: Elongation ≥ 15%; C: Charpy longitudinal impact energy at room temperature KV2 ≥ 150 J; D: Vickers hardness 490~600 HV; E: Surface Vickers hardness difference < 30 HV; F: Straightness < 1mm / m. A seamless steel tube is considered qualified if it simultaneously meets standards A to F; otherwise, it is unqualified. Table 4 lists the comprehensive mechanical property test and evaluation results of Examples 1-10 and Comparative Examples 1-6.

[0102] Table 4. Results of comprehensive mechanical property tests and evaluations for Examples 1-10 and Comparative Examples 1-6

[0103]

[0104]

[0105] As can be seen from Tables 1-4, because the seamless steel pipes in Examples 1-10 have the chemical element mass percentages specified in this invention and are manufactured according to the manufacturing method provided by this invention, their tensile strength, elongation, room temperature Charpy longitudinal impact energy KV2, Vickers hardness, surface hardness difference, and straightness all meet the comprehensive mechanical properties and dimensional accuracy requirements for seamless steel pipes used in automotive stabilizer bars. However, because the mass percentages of certain chemical elements in the steel pipes in Comparative Examples 1-6 exceed the range defined by the technical solution of this invention, or the processing technology is not carried out according to the manufacturing method provided by this invention, at least one of the comprehensive mechanical properties of these steel pipes does not meet the standard for seamless steel pipes used in automotive stabilizer bars.

[0106] Specifically, as shown in Tables 1-4, for Comparative Examples 3 and 5, the mass percentage of some chemical elements exceeds the range defined by the technical solution of this invention, and the annealing and heat preservation time of their manufacturing methods is not carried out in accordance with the manufacturing method provided by this invention, which affects their toughness and impact resistance, resulting in Comparative Examples 3 and 5 not meeting the comprehensive mechanical performance requirements of seamless steel tubes for automotive stabilizer bars.

[0107] Specifically, as shown in Tables 1-4, for Comparative Examples 1-2, although their processing technology is carried out according to the manufacturing method provided by the present invention, the mass percentage of some chemical elements exceeds the range defined by the technical solution of the present invention, affecting their tensile strength and impact performance, resulting in Comparative Examples 1-2 not meeting the comprehensive mechanical performance requirements for seamless steel tubes for automotive stabilizer bars.

[0108] As shown in Tables 1-4, although the chemical element mass percentage of Comparative Example 6 is within the range defined by the technical solution of this invention, the cold working pretreatment process of its manufacturing method is different. Specifically, the annealing and heat preservation time of its cold working pretreatment exceeds the range defined by the technical solution of this invention, resulting in Comparative Example 6 not meeting the comprehensive mechanical performance requirements of seamless steel tubes for automobile stabilizer bars.

[0109] Furthermore, as shown in Tables 1-4, in Comparative Example 4, although the mass percentage of its chemical elements is within the range defined by the technical solution of this invention, the annealing and heat preservation time of its pre-cold working treatment and the rotation speed of the steel pipe during the heat treatment of its manufacturing method exceed the range defined by the technical solution of this invention, resulting in its surface Vickers hardness difference exceeding the specified range, which does not meet the comprehensive mechanical performance requirements of seamless steel pipes for automobile stabilizer bars.

[0110] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A high-strength, high-toughness seamless steel tube for automotive anti-collision bars, characterized in that, The seamless steel pipe comprises an Fe base and chemical elements dispersed in the Fe base in the following mass percentages: C: 0.08%~0.22%, Si: 0.1%~0.45%, Mn: 1.0%~1.8%, Ni: 0.1%~0.6%, Cr: 0.05%~1.0%, Ti: 0.01%~0.05%, B: 0.005%~0.02%, Cu: 0.05%~0.50%, Al: 0.015%~0.060%, Nb: 0.01%~0.1%, N: 0.005%~0.015%. The seamless steel pipe has a tensile strength ≥1200 MPa, an elongation ≥15%, a Charpy longitudinal impact energy KV2 ≥150 J at room temperature, a Vickers hardness of 490~600 HV on the surface, and a Vickers hardness difference of <30 HV.

2. A high-strength, high-toughness seamless steel tube for automotive anti-collision bars, characterized in that, The seamless steel pipe is composed of Fe-based elements and chemical elements dispersed in the Fe-based elements in the following mass percentages: C: 0.08%~0.22%, Si: 0.1%~0.45%, Mn: 1.0%~1.8%, Ni: 0.1%~0.6%, Cr: 0.05%~1.0%, Ti: 0.01%~0.05%, B: 0.005%~0.02%, Cu: 0.05%~0.50%, Al: 0.015%~0.060%, Nb: 0.01%~0.1%, N: 0.005%~0.015%, with the balance being unavoidable impurities. The seamless steel pipe has a tensile strength ≥1200 MPa, an elongation ≥15%, a Charpy longitudinal impact energy KV2 ≥150 J at room temperature, a Vickers hardness of 490~600 HV on the surface, and a Vickers hardness difference of <30 HV.

3. The high-strength and high-toughness seamless steel tube for automotive anti-collision bars according to claim 2, characterized in that, The unavoidable impurities include P and S, wherein, by mass percentage, P ≤ 0.025% and S ≤ 0.015%.

4. The high-strength and high-toughness seamless steel tube for automotive anti-collision bars according to claim 1 or 2, characterized in that, The mass percentages of the chemical elements also satisfy the following conditions: Ti / N > 2, Nb / N > 2.

5. The high-strength and high-toughness seamless steel tube for automotive anti-collision bars according to claim 1 or 2, characterized in that, The microstructure of the seamless steel pipe consists of ferrite, pearlite, and dispersed precipitates.

6. The high-strength and high-toughness seamless steel tube for automotive anti-collision bars according to claim 5, characterized in that, The precipitated phases include Ti(CN) and Nb(CN).

7. The high-strength and high-toughness seamless steel tube for automotive anti-collision bars according to claim 1 or 2, characterized in that, The wall thickness of the seamless steel pipe is 1~2.5mm.

8. The high-strength and high-toughness seamless steel tube for automotive anti-collision bars according to claim 1 or 2, characterized in that, The outer diameter of the seamless steel pipe is 15~30mm.

9. The high-strength and high-toughness seamless steel tube for automotive anti-collision bars according to claim 1 or 2, characterized in that, The straightness of the seamless steel pipe is <0.1mm / m.

10. The method for manufacturing high-strength and high-toughness seamless steel tubes for automotive anti-collision bars according to any one of claims 1-9, characterized in that, Includes the following steps: S1, the chemical elements are proportioned according to the chemical element composition described in claim 1 or 2, and then smelted to obtain a tube blank; S2, perform hot piercing treatment on the tube blank in step S1, with a heating temperature of 1220~1260℃ and a holding time of 10~20min; S3, the tube blank after hot piercing in step S2 is placed on a tension reducing machine for diameter reduction and wall thickness reduction, and after natural cooling to room temperature, a precast steel pipe is obtained. S4, perform pretreatment on the precast steel pipe from step S3, the pretreatment including: The precast steel pipe in step S3 is subjected to pickling, annealing, phosphating and saponification in sequence. In the annealing process, the annealing temperature is 680~850℃ and the holding time is 20~70min.

11. The method according to claim 10, characterized in that, Also includes: S5, perform cold working on the prefabricated steel pipe from step S4 in one or more passes to obtain a seamless steel pipe with an outer diameter of 15~30mm and a wall thickness of 1~1.5mm, with an elongation coefficient of ≤1.8 for each pass of cold working.

12. The method according to claim 11, characterized in that, Also includes: S6, while rotating the seamless steel pipe from step S5, perform high-frequency induction hardening treatment, wherein the hardening temperature is 860~950℃, the hardening holding time is 8~20min, and then water-cooled to room temperature, the rotation speed of the seamless steel pipe is 60~150r / min, and the forward speed is 0.05~0.2m / s. The tempering temperature is 150~400℃, and after holding at this temperature for 10~40 minutes, it is air-cooled to room temperature.

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